Exemplary embodiments pertain to the art of gas turbine engines and, more particularly, to a fan case assembly for gas turbine engines.
A turbofan engine typically includes a fan, a booster, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine in serial axial flow relationship about a longitudinal centerline axis of the engine. The high pressure turbine is drivingly connected to the high pressure compressor via a first rotor shaft, and the low pressure turbine is drivingly connected to both the fan and booster via a second rotor shaft. The fan includes an annular disk and a plurality of radially extending blades mounted to the disk, where the disk and the blades are rotatable about the longitudinal centerline of the engine. Such fans are surrounded by a fan case which is specifically designed to be capable of containing a fan blade in the event that the fan blade is released from its disk during operation. This prevents or minimizes the structural damage to the engine and aircraft should one or more fan blades be released from the disk due to a failure of one or more blades, ingestion of debris, or other cause.
The fan case also serves as the outer flowpath boundary through the fan rotor and closely circumscribes the tips of the fan blades in order to minimize leakage past the fan blades. Prior fan cases are typically lined with a sacrificial abradable material in order to protect the fan blades during contact between the fan blades and the fan case (referred to as “rub”). While sacrificial wearing away of the abradable material prevents damage to costly fan blades, it also opens up the radial clearance at the blade tips, resulting in loss of engine thrust.
Current fan case rubstrip systems experience a significant amount of erosion during a prolonged period of icing. This shed ice erosion, combined with fan rotor unbalance and whirl, extends through the abradable, a septum and into the supporting structural honeycomb. In addition to the economic damage to the fan case, the eroded rubstrip allows, combined with rotor unbalance from shed ice, contribute to large fan whirl orbit. This orbit is large enough to wear the abradable in the low pressure compressor beyond allowable operational limits.